The present invention relates to monitoring of semiconductor processes. More particularly, the present invention relates to a method and apparatus to detect a fault in process conditions of a plasma-based semiconductor processing system.
Process control and diagnostics are important to determine the characteristics of films being deposited during semiconductor processing. For example, current process control and diagnostics of plasma enhanced deposition processes involve three techniques: optical endpoint detection, interferometric endpoint detection and test wafer measurement technique. The optical endpoint detection technique involves ascertaining a process endpoint by monitoring one or two narrow bands of optical emission from process plasmas. A drawback with this technique concerns the limited information regarding the characteristics of the films being deposited.
The interferometric endpoint technique takes advantage of interferometry to determine whether a film has obtained a predetermined thickness. Drawbacks associated with the interferometric endpoint technique include the limitations of materials that are suitable for use with interferometric measurements. Some materials, such as metals, do not show interferometric interference fringes unless the material being measured is extremely thin. Secondly, the interferometric technique does not predict true process endpoints.
The test wafer measurement technique involves direct measurement of a film disposed on a substrate. As a result, the test wafer measurement technique evaluates the last process step performed by examination of test wafers that are processed within a group of production wafer. This is a drawback, because this technique does not identify failures of intermediate process steps. This may result in the loss of a great number of processed wafers. In addition, the test wafer measurement technique is destructive in nature, substantially reducing the operational life of the test wafer.
Recent advancements have been made in monitoring of semiconductor etch processes employing spectroscopic techniques. For example, in U.S. Pat. No. 6,068,783 to Szetsen, a spectroscopic method is disclosed for selecting a single plasma gas as a probe, in a cleaned plasma etch chamber; measuring the spectral intensities of the plasma gas; and plotting the measured spectral intensities either directly or indirectly against the RF time. In this manner, a single plasma gas is selected which exhibits opposite relationships with RF time at two respective wavelengths to facilitate in-situ monitoring of the etching process.
In U.S. Pat. No. 5,877,032 to Guinn et al. a process is disclosed in which a plasma containing a fluorocarbon gas is monitored using optical emission spectroscopy to effect control of an etch process. To control the process based on an observation of photoresist etch rate, two wavelengths are monitored. One wavelength is associated with a species, that is produced by the interaction between the photoresist and the plasma, and one wavelength is associated with a species related to the plasma intensity. The ratio of the optical intensity at these two wavelengths is determined in real time processing, and the ratio is associated with acceptable process conditions by referring to a predetermined calibration curve that associates a particular ratio with a particular photoresist etch rate for a given set of process conditions. Were the ratio observed not to be within a certain range of ratios determined to indicate acceptable process conditions, the plasma conditions are either changed to bring the ratio back within the desired range, or the process is stopped until the problem is corrected. To control the process based on an observation of contact hole etch rate, a wavelength associated with one species in the plasma is monitored at two different times during the etch process. A ratio of the measured intensity at these two different times is obtained. Calibration information is then used to determine if the ratio indicates that the process is proceeding acceptably. If the ratio is not within the acceptable range, remedial action is taken. However, the information obtained from the aforementioned spectroscopic techniques is limited in its ability to detect and classify faults that occur during the process.
What is needed, therefore, is a technique to detect and classify faults during processing of a substrate in a semiconductor process.
Provided are a method and an apparatus that feature detecting faults in process conditions of a plasma-based semiconductor processing system by sensing the spectral emissions of the plasma. The method includes sensing optical energy produced by the plasma and identifying the faulting the process conditions as a function of one or more of the plurality of spectral bands. Specifically, the optical energy has a plurality of spectral bands associated therewith, and a subset of the spectral bands includes information corresponding to one or more faults that may occur in the process conditions of the processing chamber. Examples of the process conditions which may cause faults include incorrect pressurization of the processing chamber, degradation of optical data paths, arcing between the substrate and an electrode, incorrect film being deposited on the substrate, the substrate not being properly situated on a pedestal and the like. Various techniques are employed to identifying the aforementioned faults from the subset of spectral bands, including identifying variations in the total intensity or identifying a ratio between multiple subsets of the spectral bands. In addition, detailed information that correlates the fault with the subsystem of the processing system that causes the same is achieved by analyzing the aforementioned subsets of spectral bands, as well as spectral bands containing information concerning the characteristics of a film being deposited. The apparatus includes a detector in optical communication with the processing chamber to sense optical energy generated by the plasma, and a spectrum analyzer, in electrical communication with the optical detector. The spectrum analyzer resolves the spectral bands and produces information corresponding thereto. A processor is in electrical communication with the spectrum analyzer, and a memory is in electrical communication with the processor. The memory includes a computer-readable medium having a computer-readable program embodied therein that controls the system to carry-out the method.